From 054f1d1faaed6a7930b77286d607ae45c01d0443 Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Thu, 11 Jul 2019 20:55:37 -0700 Subject: mm/swap_state.c: simplify total_swapcache_pages() with get_swap_device() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit total_swapcache_pages() may race with swapper_spaces[] allocation and freeing. Previously, this is protected with a swapper_spaces[] specific RCU mechanism. To simplify the logic/code complexity, it is replaced with get/put_swap_device(). The code line number is reduced too. Although not so important, the swapoff() performance improves too because one synchronize_rcu() call during swapoff() is deleted. [ying.huang@intel.com: fix bad swap file entry warning] Link: http://lkml.kernel.org/r/20190531024102.21723-1-ying.huang@intel.com Link: http://lkml.kernel.org/r/20190527082714.12151-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" Reviewed-by: Andrew Morton Tested-by: Mike Kravetz Cc: Hugh Dickins Cc: Paul E. McKenney Cc: Minchan Kim Cc: Johannes Weiner Cc: Tim Chen Cc: Mel Gorman Cc: Jérôme Glisse Cc: Michal Hocko Cc: Andrea Arcangeli Cc: Yang Shi Cc: David Rientjes Cc: Rik van Riel Cc: Jan Kara Cc: Dave Jiang Cc: Daniel Jordan Cc: Andrea Parri Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 33 +++++++++++++++------------------ 1 file changed, 15 insertions(+), 18 deletions(-) (limited to 'mm') diff --git a/mm/swap_state.c b/mm/swap_state.c index 61453f1faf72..8368621a0fc7 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -73,23 +73,24 @@ unsigned long total_swapcache_pages(void) unsigned int i, j, nr; unsigned long ret = 0; struct address_space *spaces; + struct swap_info_struct *si; - rcu_read_lock(); for (i = 0; i < MAX_SWAPFILES; i++) { - /* - * The corresponding entries in nr_swapper_spaces and - * swapper_spaces will be reused only after at least - * one grace period. So it is impossible for them - * belongs to different usage. - */ - nr = nr_swapper_spaces[i]; - spaces = rcu_dereference(swapper_spaces[i]); - if (!nr || !spaces) + swp_entry_t entry = swp_entry(i, 1); + + /* Avoid get_swap_device() to warn for bad swap entry */ + if (!swp_swap_info(entry)) + continue; + /* Prevent swapoff to free swapper_spaces */ + si = get_swap_device(entry); + if (!si) continue; + nr = nr_swapper_spaces[i]; + spaces = swapper_spaces[i]; for (j = 0; j < nr; j++) ret += spaces[j].nrpages; + put_swap_device(si); } - rcu_read_unlock(); return ret; } @@ -611,20 +612,16 @@ int init_swap_address_space(unsigned int type, unsigned long nr_pages) mapping_set_no_writeback_tags(space); } nr_swapper_spaces[type] = nr; - rcu_assign_pointer(swapper_spaces[type], spaces); + swapper_spaces[type] = spaces; return 0; } void exit_swap_address_space(unsigned int type) { - struct address_space *spaces; - - spaces = swapper_spaces[type]; + kvfree(swapper_spaces[type]); nr_swapper_spaces[type] = 0; - rcu_assign_pointer(swapper_spaces[type], NULL); - synchronize_rcu(); - kvfree(spaces); + swapper_spaces[type] = NULL; } static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma, -- cgit v1.2.3